Large enterprises typified by banks, securities companies, telephone companies, and so on tend to reduce expenses required for operation, maintenance, and management of a computer system and a storage system by configuring the computer system and the storage system such that computers and storages, which have been conventionally dispersed in various placed, are concentrated in a data center, and it is specifically demanded that mainframe/high-end storage system support a channel interface for connection to several hundreds or more of host computers (connectivity) and storage capacity of several hundreds or more tera-bytes.
Furthermore, progress in information-oriented society has no bounds to a rapid increase in amount of communication and data. However, due to an unpredictable increase in amount of data, physical extension increases cost and labor required for operation, maintenance, and management of a storage system.
Hereupon, free system configurations meeting with various needs have recently been demanded of as a storage pool by needs of users, and among these configurations, it has been demanded to construct a virtual volume so as to make effective use of a vacant capacity between a plurality of storages.
Also, for the sake of maintenance, a demand has been made for extendability, such as flexibility or the like, enabling construction of highly reliable configuration modules, a clustered system, a highly available system produced by a system construction technique to combine them, and a system meeting customer's needs and enabling easily accommodating extension and configurational modification, and operativity of compressing a total storage capacity and facilitating extension and configurational modification.
Conventionally, there has been a structure, in which a plurality of host computers and disk storage units are connected to each other through a switch router as shown in, for example, FIG. 23 and a plurality of host computers and disk storage units are connected to each other through fiber channels as shown in, for example, FIG. 24.
Under present circumstances, extension of volume is not achieved until setting is modified and corrected on a user's side, but restrictions due to operating system (OS) and middle ware lead to damage to open quality and extension on a user's part, and in order to perform a flexible and dynamic modification on time, cost is small in operation when such modification is autonomously enabled on a storage unit side.
However, a conventional disk array system shown in FIG. 23 involves a problem that since correspondence between host computers and disk storage units is fundamentally 1 versus 1 and maintenance must be performed in respective units when a single disk storage unit is an obstacle to cause incapability of storage of data, or insufficiency of capacity causes incapability of storage of data, there is a need of modifying an address to a separate unit to change a data storage place, and a configuration shown in FIG. 24 involves a problem that while disaster recovery such as backup and restoration of a virtual volume is demanded in order to prevent a data center from being paralyzed due to sudden accidents, an increase in standing operating cost and complexity in management are made unavoidable by newly installing an increased groups of disk storage units and management units for managing them, or storage switches.